Basics of Geo-thermal Power

There’s a very simple reason the “experts” suggest installing a wind/solar energy hybrid system, especially for off the grid living. Historically, in the United States, weather patterns fluctuate, summer … strong solar … weak winds. Winter … weak solar … strong winds. This fluctuation provides reliable green energy year round. There is another year round energy source.

Simple Geo-thermal theory explanation: The United States experiences a wide spectrum of weather conditions from blazing heat to frigid sub-zero cold, Most times in the same city or state. However, just a few feet under the earth’s surface the ground temperature remains relatively the same regardless of surface temperatures. This constant 45/7 to 75/21 degree F or C, is the source of heat we will tap into in order to create a Geo-thermal heating and cooling system.

Geo-thermal – Benefits

Geo-thermal energy taps into the earth’s sub-surface to harness the earth’s natural heat, thus creating a renewable and literally zero green house gases. How can that be? Geo-thermal systems heat and cool the home with for all practical purposes, virtually no electrical power, no need to create large amounts of electricity means no carbon footprint, making the process extremely Eco-friendly.

As a Geo-thermal unit maintains @50% relative indoor humidity they are effective in all environments, from humid Florida to bone dry Arizona.

Geo-thermal heat pump systems are extremely flexible and can be designed to be installed in both new and retro fit construction.

Something most people overlook, whether in new construction design or retro fit, is the space required to house a conventional HAVC system. It is substantial especially if space is at a premium. The equipment required for a Geo-thermal system is quite small freeing space for alternative uses.

Perhaps the most important aspect, especially for the average homeowner, is the durability and reliability of the system. Geo-thermal systems have very few moving parts, and those that do move are located inside the house away from the elements, requiring little to no maintenance. Additionally, the system is so quiet no one at home will know when it’s running.

What Next? Evaluating Your Home

A brief description of Geo-thermal variables

Although a Geo-thermal system can be installed literally anywhere in the world, there are variables that will greatly effect the type and degree of difficulty required to install the unit. If your contractor doesn’t agree … fire him before you hire him.

Geological factors, such as the properties and composition of your soil may have a large impact on the type of geothermal system you choose to install. Soil with good heat transfer properties will require less piping than poor heat transfer soil. Areas with extensive rock content or incredibly difficult to trench may be forced to install a vertical loop system instead of a horizontal ground loop system.

Hydrology refers to the surface water availability which affects the type of Geo-thermal ground loop to use. Factors such as depth, water quality, volume and surface area can be imperative in deciding if an open loop system, or a repository for coils of piping for a closed loop system is possible.

The size of usable land can dictate your system. Horizontal ground loop systems are the least expensive to install, but existing landscaping, sprinkler systems or underground utilities may force the installation of a vertical loop system.

Types of Geo-thermal Heat Pump Systems

Unless you are familiar with Geo-thermal you are probably quite sick of hearing about looped systems you have no concept of. We will now delve a little more into the complexities of these different systems.

There are four basic types of ground loop systems, horizontal, vertical and pond/lake systems which are known as closed loop systems … the fourth is an open loop system. Any of the four can be used for residential or commercial use, but climate, soil conditions, land size and local labor cost will dictate which would be the best for the particular installation.

Let’s begin with the Closed Loop System

Nearly all 98% of closed-loop heat pumps circulate an anti-freeze solution through specially designed plastic tubing, which is buried underground or submerged in deeper water in a closed loop system. This antifreeze is run through a heat ex-changer that transfers the heat between the anti-freeze and the heat pump.

Another variation is called a direct exchange, that does not include a heat ex-changer, but rather pumps the refrigerant through copper coils that are buried in the ground, either horizontally or vertically. There are some complications with this system, as a much larger compressor is required, costing more to run and maintain. Additionally the soil must have a high moisture content which may require adding a sprinkler system. Lastly, certain soils, such as a high content of limestone, are very corrosive to copper increasing the chances of a leak being created.

heat transfer diagram

This type of installation for residential homes is preferred due to the cost effectiveness of the installation. It requires the excavation of trenches, one minimum of four feet deep, for 1 pipe to lay in, the second at least six feet deep for the second pipe. A variation of this installation is to dig a five foot deep by 2 foot wide trench, and lay the piping in a slinky method, looping the tubing. This has several advantages, for example it reduces the size and amount of trenching as the slinky method allows more pipe to be placed in a smaller area, which may allow this less expensive method to be used when originally thought there wasn’t enough usable land available.

Vertical System


Large commercial buildings and schools will nearly always utilize a vertical system because the amount of piping required would demand extensive trenching over a large tract of land, which is normally not available or very expensive. Vertical systems can also be used when there isn’t enough soil over bedrock for deep enough and proper trenching. Installation requires a trench to be dug to hold a horizontal pipe, known as a manifold which connects the vertical piping to the equipment stored inside the building. Depending on the requirements, four inch diameter holes are drilled to 100 to 400 feet deep and 20 feet apart. Pipes are inserted into these holes, with a U-bend connection which redirects the pipe back up the hole to the manifold.

inapondWater-source System

The pond/lake system as its known is by far the cheapest of all installations and is ideal for a cabin or vacation home, although it can be utilized for a full time residence. Installation is simple, a trench is dug from the house to the water source, beneath the freeze line, a pipe is inserted and covered with soil. The pipe will be fished into the water source, how far out depends on the size of the pond/lake, and must be coiled and sunk to a minimum of eight feet beneath the surface. Caution: You must monitor the depth of the water if there is any doubt that lack of rainfall could create an unsafe water level.

Open Loop System

This system, which in my opinion is the least desirable, uses well or surface water as the heat exchange fluid that circulates through the GHO system, then returns to the well or to a surface discharge. This option can only be used when there is an unlimited amount of clean water and groundwater discharge is not a violation of state or local rules or regulations.

Geo-thermal heat pumps (GHP) are not a new craze, they have been in use since the 1940s, of course there have been huge technological advances as with any other technology. Going “green” is a personal choice, but sometimes its largely dictated by cost, and that depends on how you describe cost. The Geo-thermal system may cost as much as 3 or 4 times a traditional HAVC system, however the reduced costs of operation may pay for itself in as little as 5 to 10 years. The system’s expected life span is 25 years for inside components and 50+ years for the ground loop.


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